Water Model Research Articles

Understanding of Anion Effect on Iron Redox Behavior and Oxygen Reduction Activity of Fe-N-C Electrocatalysts

Fe-N-C catalysts are the most promising platinum group metal (PGM) free electrocatalysts for oxygen reduction reaction (ORR). Significant progress has been made in understanding the active site structure and activity and improving the ORR performance. It is generally accepted that the Fe-N-C sites are associated with FeNx centers embedded in a defective nitrogen-doped graphene. As reported in literature, both pyrrolic N and pyridinic N can support Fe single site; however, it is difficult to distinguish between the two. Furthermore, experimental characterization, such as in-situ X-ray absorption spectroscopy (XAS) and Mössbaruer, has elucidated the redox behavior of Fe2+ to Fe3+ during the reaction. Interestingly, in different acidic environments, the ORR activity exhibits differently. For instance, in comparison between H2SO4 and HClO4 solutions at the same pH value, the Fe redox happens at lower potential in H2SO4; however, the right shift of half-wave potential (E1/2) of ORR in H2SO4, compared with HClO4, indicates higher ORR activity. This indicates that the electrolyte systems have a significant impact on ORR activity. To further understand the active site structure and their ORR activity, density functional theory (DFT) calculations utilizing explicit solvation effect are carried out. XANES simulation using FDMNES suggests that as prepared catalysts could consist of Fe single atom sites supported by both pyrrolic and pyridinic N atoms; however, the pyrrolic species are not as stable as pyridinic species in solution. As presented by DFT simulation, the anions in solutions can interact with FeN4 site differently. SO4 2- binds strongly with the FeN4 center, while HSO4- and ClO4- interact rather weakly. Furthermore, the redox potential and limiting potential are evaluated via mechanistic study. By focusing on more stable Fe center supported by pyridinic N, the results suggest that the transformation of Fe2+ to Fe3+ happens at 0.52 V in H2SO4, which is lower than that in HClO4, 0.69V. More interestingly, the limiting potential (activity) of ORR in H2SO4 is higher than that in HClO4 (0.94 vs 0.68 V). DFT simulation indicated that the anions in electrolyte can impact the Fe redox behavior and ORR performance, which agrees well with the experimental investigation. This work also provides significant guidance to further improve ORR activity of Fe-N-C catalysts.

Papain-Mediated Conjugation of Peptide Nucleic Acids to Delivery Peptides: A Density Functional Theory/Molecular Mechanics Metadynamics Study in Aqueous and Organic Solvent.

Enzymatic peptide synthesis is a powerful alternative to solid-phase methods, as enzymes can have high regio- and stereoselectivity and high yield and require mild reaction conditions. This is beneficial in formulation research due to the rise of nucleic acid therapies. Peptide nucleic acids (PNAs) have a high affinity toward DNA and RNA, and their solubility and cellular delivery can be improved via conjugation to peptides. Here, we designed and assessed the viability of the papain enzyme to conjugate four PNA-peptide models in water and an organic solvent using QM/MM metadynamics. We found that the reactions in water yield better results, where three conjugates could potentially be synthesized by the enzyme, with the first transition state as the rate-limiting step, with an associated energy of 14.53 kcal mol-1, although with a slight endergonic profile. The results highlight the importance of considering the enzyme pockets and different substrate acceptivities and contribute to developing greener, direct, and precise synthetic routes for nucleic acid-based therapies. By exploring the enzyme's potential in conjunction with chemical synthesis, current protocols can be simplified for the synthesis of longer nucleic acids and peptide sequences (and, by extension, proteins) from smaller oligo or peptide blocks.

Hybrid Cluster-Continuum Method for Single-Ion Solvation Free Energy in Acetonitrile Solvent.

A new hybrid discrete-continuum approach named the cluster-continuum static approximation (CCSA) has been proposed for acetonitrile solvent. The continuum part uses the conductor-like polarizable continuum model for electrostatic and a surface area-dependent term for nonelectrostatic solvation. The CCSA includes only one explicit acetonitrile solvent molecule and a damping function, which makes the CCSA method reduce to pure continuum solvation in the case of weaker potential of mean force for solute-solvent interaction. The performance of the model was tested for 22 anions and 22 cations, including challenge species that cannot be adequately described by pure continuum solvation. A comparison was done with the widely used solvent model density (SMD) model. For anions, the CCSA reduces to pure continuum solvation and the method has the same performance as the SMD model, with a standard deviation of the mean signed error (SD-MSE) of 2.7 kcal mol-1 for both models. However, the CCSA method for cations considerably outperforms the SMD model, with an SD-MSE of 3.3 kcal mol-1 for the former and 8.4 kcal mol-1 for the latter. The method can be automated, and the present study suggests that continuum solvation models could be parameterized taking into account the explicit solvation as proposed in this work.

Registry alteration in Dynein's microtubule-binding domain: A AAA domain-guided event

Dynein, a motor protein, harnesses chemical energy from ATP hydrolysis to generate mechanical output as it travels along microtubular tracks. Essential to this process is the microtubule-binding domain (MTBD), which facilitates the interaction with and detachment from microtubules. Previous studies have proposed that the mechanism governing this interaction is primarily driven by the coiled-coil stalk attached to the MTBD. However, conflicting arguments suggest the presence of two-way communications, where the binding and unbinding mechanisms may also influence the nucleotide state of dynein. In this study, we employed all-atom explicit solvent simulations, enhanced sampling techniques, and coarse-grained methodologies to systematically investigate the effects of stalk and MT on the structural stabilities of different conformations of MTBD and their sequence of events during the transition from one to another. We found that the globular MTBD domain without stalk and MT predominantly resides in its weak binding configuration. Upon introduction of a limited length of stalk and interaction with MT, a balance between the strong and weak binding configurations is restored. Further introduction of the full-length stalk and interaction with MT strengthen the kinetic stability of these two configurations. We have also explored the sequence of events of the relevant transition between these two states using coarse-grained simulation protocols both in the presence and absence of interaction with MT. In the absence of MT interactions, we found a mixed conformational state of the system that corresponds to the already published crystal structure of Dynein. In the presence of MT, the conformational change of the stalk precedes the conformational change of the MTBD globular domain. Our findings support the view that the nucleotide state of the AAA+ ring determines the state of the MTBD domain through stalk, shedding light on the intricate mechanisms governing dynein's interaction with microtubules.

Dissociation line and driving force for nucleation of the nitrogen hydrate from computer simulation. II. Effect of multiple occupancy.

In this work, we determine the dissociation line of the nitrogen (N2) hydrate by computer simulation using the TIP4P/Ice model for water and the TraPPE force field for N2. This work is the natural extension of Paper I, in which the dissociation temperature of the N2 hydrate has been obtained at 500, 1000, and 1500bar [Algaba et al., J. Chem. Phys. 159, 224707 (2023)] using the solubility method and assuming single occupancy. We extend our previous study and determine the dissociation temperature of the N2 hydrate at different pressures, from 500 to 4500bar, taking into account the single and double occupancy of the N2 molecules in the hydrate structure. We calculate the solubility of N2 in the aqueous solution as a function of temperature when it is in contact with a N2-rich liquid phase and when in contact with the hydrate phase with single and double occupancy via planar interfaces. Both curves intersect at a certain temperature that determines the dissociation temperature at a given pressure. We observe a negligible effect of occupancy on the dissociation temperature. Our findings are in very good agreement with the experimental data taken from the literature. We have also obtained the driving force for the nucleation of the hydrate as a function of temperature and occupancy at several pressures. As in the case of the dissociation line, the effect of occupancy on the driving force for nucleation is negligible. To the best of our knowledge, this is the first time that the effect of the occupancy on the driving force for nucleation of a hydrate that exhibits sII crystallographic structure is studied from computer simulation.

Donnan equilibrium in charged slit-pores from a hybrid nonequilibrium molecular dynamics/Monte Carlo method with ions and solvent exchange.

Ion partitioning between different compartments (e.g., a porous material and a bulk solution reservoir), known as Donnan equilibrium, plays a fundamental role in various contexts such as energy, environment, or water treatment. The linearized Poisson-Boltzmann (PB) equation, capturing the thermal motion of the ions with mean-field electrostatic interactions, is practically useful to understand and predict ion partitioning, despite its limited applicability to conditions of low salt concentrations and surface charge densities. Here, we investigate the Donnan equilibrium of coarse-grained dilute electrolytes confined in charged slit-pores in equilibrium with a reservoir of ions and solvent. We introduce and use an extension to confined systems of a recently developed hybrid nonequilibrium molecular dynamics/grand canonical Monte Carlo simulation method ("H4D"), which enhances the efficiency of solvent and ion-pair exchange via a fourth spatial dimension. We show that the validity range of linearized PB theory to predict the Donnan equilibrium of dilute electrolytes can be extended to highly charged pores by simply considering renormalized surface charge densities. We compare with simulations of implicit solvent models of electrolytes and show that in the low salt concentrations and thin electric double layer limit considered here, an explicit solvent has a limited effect on the Donnan equilibrium and that the main limitations of the analytical predictions are not due to the breakdown of the mean-field description but rather to the charge renormalization approximation, because it only focuses on the behavior far from the surfaces.

Machine learning based aerosol and ocean color joint retrieval algorithm for multiangle polarimeters over coastal waters

NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, recently launched in February 2024, carries two multiangle polarimeters (MAPs): the UMBC Hyper-Angular Rainbow Polarimeter (HARP2) and SRON Spectropolarimeter for Planetary Exploration One (SPEXone). Measurements from these MAPs will greatly advance ocean ecosystem and aerosol studies as their measurements contain rich information on the microphysical properties of aerosols and hydrosols. The Multi-Angular Polarimetric Ocean coLor (MAPOL) joint retrieval algorithm has been developed to retrieve aerosol and ocean color information, which uses a vector radiative transfer (RT) model as the forward model. The RT model is computationally expensive, which makes processing a large amount of data challenging. FastMAPOL was developed to expedite retrieval using neural networks to replace the RT forward models. As a prototype study, FastMAPOL was initially limited to open ocean applications where the ocean Inherent Optical Properties (IOPs) were parameterized in terms of one parameter: chlorophyll-a concentration (Chla). In this study we further expand the FastMAPOL joint retrieval algorithm to incorporate NN based forward models for coastal waters, which use multi-parameter bio-optical models. In addition, aerosols are represented by six components, i.e., fine mode non absorbing insoluble (FNAI), brown carbon (BrC), black carbon (BC), fine mode non absorbing soluble (FNAS), sea salt (SS) and non-spherical dust (Dust). Sea salt and dust are coarse mode aerosols, while the other components are fine mode. The sizes and spectral refractive indices are fixed for each aerosol component, while their abundances are retrievable. The multi-parameter bio-optical model and aerosol components are chosen to represent the coastal marine environment. The retrieval algorithm is applied to synthetic measurements in three different configurations of MAPs in the PACE mission: HARP2 observations only, SPEXone observations only and combined HARP2 and SPEXone observations. The retrieval results from synthetic measurements show that for aerosol retrieval the SPEXone-only configuration works equally well with the HAPR2-only configuration. On the other hand, for ocean color retrieval the SPEXone instrument provides better information due to its larger spectral coverage. For the surface parameters (wind speed), HARP2 measurements provide better information due to its wide field of view. Combined measurement configuration HARP2+SPEXone performed the best to retrieve all aerosol, ocean color, and surface parameters. We also studied the impact of sun glint to aerosol and ocean color retrievals. The retrieval test revealed that wind speed and absorbing aerosol retrieval improves significantly when including measurements at glint geometries. Furthermore, the retrieval algorithm is equipped with modules for atmospheric correction and bidirectional reflectance distribution (BRDF) correction to obtain the remote sensing reflectance, which enables ocean biogeochemistry studies using the PACE polarimeter data.

Derivation and numerical resolution of 2D shallow water equations for multi-regime flows of Herschel–Bulkley fluids

This paper presents mathematical modelling and simulation of thin free-surface flows of viscoplastic fluids with a Herschel–Bulkley rheology over complex topographies with basal perturbations. Using the asymptotic expansion method, depth-averaged models (lubrication and shallow water type models) are derived for 3D (three-dimensional) multi-regime flows on non-flat inclined topographies with varying basal slipperiness. Starting from the Navier–Stokes equations, two flow regimes corresponding to different balances between shear and pressure forces are presented. Flow models corresponding to these regimes are calculated as perturbations of the zeroth-order solutions. The classical reference models in the literature are recovered by considering their respective cases on a flat-inclined surface. In the second regime case, a pressure term is non-negligible. Mathematically, it leads to a corrective term to the classical regime equations. Flow solutions of the two regimes are compared; the difference appears in particular in the vicinity of sharp changes of slopes. Nonetheless, both regime models are compared with experiments and are found to be in good agreement. Furthermore, numerical examples are shown to illustrate the robustness of the present shallow water models to simulate viscoplastic flows in 3D and over an inclined topography with local perturbations in basal elevation and basal slipperiness. The derived models are adequate for direct (engineering and geophysical) applications to real-world flow problems presenting Herschel–Bulkley rheology like lava and mud flows.

The phase diagram of Mercedes Benz model of water using nested sampling algorithm and molecular dynamics simulations

The Mercedes Benz (MB) model of water is quite popular for explaining the properties of water, but the complete phase diagram has not yet been published. In the MB model, water molecules are modelled as two-dimensional Lennard-Jones discs, with three orientation-dependent hydrogen-bonding arms arranged as in the MB logo. Nested Sampling (NS) is a powerful sampling algorithm for the parameter space that directly calculates the partition function. NS can be used for sampling the equilibrium thermodynamics of atomistic systems and allows access to all thermodynamic quantities in absolute terms, including absolute free energies and absolute entropies. Here, NS is used to calculate the phase diagram of the simple two-dimensional Mercedes-Benz (MB) model of water. 32 water particles were used in NS. While this number of particles provides sufficient agreement with the simulations, the results from fewer particles slowly begin to diverge from the result from NS with 32 particles as some of the equilibrium lines begin to shift. By combining the results from NS and molecular dynamics (MD) simulations, different phases were located and identified. In total, 5 different solid phases, 3 liquid phases and one gaseous phase were observed.

Wind and rain compound with tides to cause frequent and unexpected coastal floods

With sea-level rise, flooding in coastal communities is now common during the highest high tides. Floods also occur at normal tidal levels when rainfall overcomes stormwater infrastructure that is partially submerged by tides. Data describing this type of compound flooding is scarce and, therefore, it is unclear how often these floods occur and the extent to which non-tidal factors contribute to flooding. We combine measurements of flooding on roads and within storm drains with a numerical model to examine processes that contribute to flooding in Carolina Beach, NC, USA – a community that chronically floods outside of extreme storms despite flood mitigation infrastructure to combat tidal flooding. Of the 43 non-storm floods we measured during a year-long study period, one-third were unexpected based on the tidal threshold used by the community for flood monitoring. We introduce a novel model coupling between an ocean-scale hydrodynamic model (ADCIRC) and a community-scale surface water and pipe flow model (3Di) to quantify contributions from multiple flood drivers. Accounting for the compounding effects of tides, wind, and rain increases flood water levels by up to 0.4 m compared to simulations that include only tides. Setup from sustained (non-storm) regional winds causes deeper, longer, more extensive flooding during the highest high tides and can cause floods on days when flooding would not have occurred due to tides alone. Rainfall also contributes to unexpected floods; because tides submerge stormwater outfalls on a daily basis, even minor rainstorms lead to flooding as runoff has nowhere to drain. As a particularly low-lying coastal community, Carolina Beach provides a glimpse into future challenges that coastal communities worldwide will face in predicting, preparing for, and adapting to increasingly frequent flooding from compounding tidal and non-tidal drivers atop sea-level rise.

Communication—First-Principles Simulations of LiPF6 Decomposition in Ethylene Carbonate-Based Electrolytes

We revisit a theoretical result by Okamoto (2013 Journal of The Electrochemical Society, 160, A404) who calculated the energy barrier for the decomposition of lithium hexafluorophosphate (LiPF6) into LiF + PF5 when solvated in Ethylene carbonate (EC)-based electrolyte. Using different numerical techniques to discretize the Density Functional Theory (DFT) equations, and different continuum solvation models with the same dielectric constant, our results largely confirm the original calculation. However, simulations with a higher dielectric permittivity value, closer to that of EC, show a lower energy barrier. More importantly, First-Principles simulations with an explicit solvent show a substantially lower energy barrier.

A Comprehensive Study of Factors Affecting the Prediction of the pKa Shift of Asp26 in Thioredoxin Protein.

The stable protonation state of ionizable amino acids in a protein can be predicted by computing the pKa shift of that residue within the protein environment. Thermodynamic Integration (TI) is an ideal molecular dynamics-based approach for predicting the pKa shift of ionizable protein residues. Here, we probe TI-based simulation protocols for their ability to accurately predict the pKa shift of Asp26 in thioredoxin. While implicit solvent models can predict the pKa shift accurately, explicit solvent models result in substantial errors. To understand the underlying reason for this surprising discrepancy, we investigate the role of various factors such as solvent models, conformational sampling, background charges, and polarization.

The Role of Forcing and Parameterization in Improving Snow Simulation in the Upper Colorado River Basin Using the National Water Model

AbstractThis study assesses snow water equivalent (SWE) simulation uncertainty in the National Water Model (NWM) due to forcing and model parameterization, using data from 46 Snow Telemetry (SNOTEL) sites in the Upper Colorado River Basin (UCRB). We evaluated the newly developed Analysis of Record for Calibration (AORC) forcing data for SWE simulation and examined the impact of bias correction applied to AORC precipitation and temperature. Additionally, we investigated the sensitivity of SWE simulations to choices of physical parameterization schemes through 72 ensemble experiments. Results showed that NWM driven by AORC forcings captured the overall temporal variation of SWE but underestimated its amount. Adjusting AORC precipitation with SNOTEL observations reduced SWE root‐mean‐square error (RMSE) by 66%, adjusting temperature trimmed it by 10%, and adjusting both decreased it by 69%. Among the physical processes, the snow/soil temperature time scheme (STC) demonstrated the highest sensitivity, followed by the surface exchange coefficient for heat (SFC), snow surface albedo (ALB), and rainfall and snowfall partitioning (SNF), while the lower boundary of soil temperature (TBOT) proved to be insensitive. Further optimization of the parameterization combination resulted in a 12% SWE RMSE reduction. When combined with the bias‐corrected AORC precipitation and temperature, this optimization led to a remarkable 78% SWE RMSE reduction. Despite these enhancements, a persistent slow and late spring ablation suggests model deficiencies in snow ablation physics. The study emphasizes the critical need to enhance the accuracy of forcing data in mountainous regions and address model parameterization uncertainty through optimization efforts.

The existence and uniqueness of weak solutions for a highly nonlinear shallow-water model with Coriolis effect

In this paper, we consider the Cauchy problem for a highly nonlinear shallow water model arising from the full water waves with Coriolis effect. The existence of weak solutions to the equation in the lower order Sobolev space Hs(R) with 1<s≤32 is presented. Moreover, the local well-posedness of strong solutions in Sobolev space Hs(R) with s>32 is established by the pseudoparabolic regularization technique.

Advanced sampling simulations of coupled folding and binding of phage P22 N-peptide to boxB RNA

Protein-RNA interactions are crucially important for numerous cellular processes and often involve coupled folding and binding of peptide segments upon association. The Nut-utilization site (N)-protein of bacteriophages contains an N-terminal arginine-rich motif that undergoes such a folding transition upon binding to the boxB RNA hairpin loop target structure. Molecular dynamics free energy simulations were used to calculate the absolute binding free energy of the N-peptide of bacteriophage P22 in complex with the boxB RNA hairpin motif at different salt concentrations and using two different water force field models. We obtained good agreement with experiment also at different salt concentrations for the TIP4P-D water model that has a stabilizing effect on unfolded protein structures. It allowed us to estimate the free energy contribution resulting from restricting the molecules’ spatial and conformational freedom upon binding, which makes a large opposing contribution to binding. In a second set of umbrella sampling simulations to dissociate/associate the complex along a separation coordinate, we analyzed the onset of preorientation of the N-peptide and onset of structure formation relative to the RNA and its dependence on the salt concentration. Peptide orientation and conformational transitions are significantly coupled to the first contact formation between peptide and RNA. The initial contacts are mostly formed between peptide residues and the boxB hairpin loop nucleotides. A complete transition to an α-helical bound peptide conformation occurs only at a late stage of the binding process a few angstroms before the complexed state has been reached. However, the N-peptide orients also at distances beyond the contact distance such that the sizable positive charge points toward the RNA’s center-of-mass. Our result may have important implications for understanding protein- and peptide-RNA complex formation frequently involving coupled folding and association processes.

Simulating Metal-Imidazole Complexes.

One commonly observed binding motif in metalloproteins involves the interaction between a metal ion and histidine's imidazole side chains. Although previous imidazole-M(II) parameters established the flexibility and reliability of the 12-6-4 Lennard-Jones (LJ)-type nonbonded model by simply tuning the ligating atom's polarizability, they have not been applied to multiple-imidazole complexes. To fill this gap, we systematically simulate multiple-imidazole complexes (ranging from one to six) for five metal ions (Co(II), Cu(II), Mn(II), Ni(II), and Zn(II)) which commonly appear in metalloproteins. Using extensive (40 ns per PMF window) sampling to assemble free energy association profiles (using OPC water and standard HID imidazole charge models from AMBER) and comparing the equilibrium distances to DFT calculations, a new set of parameters was developed to focus on energetic and geometric features of multiple-imidazole complexes. The obtained free energy profiles agree with the experimental binding free energy and DFT calculated distances. To validate our model, we show that we can close the thermodynamic cycle for metal-imidazole complexes with up to six imidazole molecules in the first solvation shell. Given the success in closing the thermodynamic cycles, we then used the same extended sampling method for six other metal ions (Ag(I), Ca(II), Cd(II), Cu(I), Fe(II), and Mg(II)) to obtain new parameters. Since these new parameters can reproduce the one-imidazole geometry and energy accurately, we hypothesize that they will reasonably predict the binding free energy of higher-level coordination numbers. Hence, we did not extend the analysis of these ions up to six imidazole complexes. Overall, the results shed light on metal-protein interactions by emphasizing the importance of ligand-ligand interaction and metal-π-stacking within metalloproteins.

Calculated Aqueous Reduction Potentials of Neutral and Anionic Halogen Diatomic Molecules.

The free energy of hydration, aqueous, and gas phase electron affinity and aqueous reduction potentials of F2, Cl2, Br2, I2, ClF, BrF, IF, BrCl, ICl, IBr, and their corresponding anions were calculated using an electronic structure approach previously developed for these properties for X• and XO•, where X is a halogen which yielded excellent results. The gas phase electron affinities were calculated at the Feller-Peterson-Dixon level based on complete basis set extrapolation of CCSD(T) results with additional corrections. The agreement with the available experimental data is excellent, and the calculations provide a complete set of reliable electron affinities for these diatomic halogens. The hybrid solvation approach uses single point implicit solvation calculations on gas phase optimized clusters with explicit solvent molecules. The gas phase energy calculations were performed using MP2 and CCSD(T)-F12b for tetramer clusters (four explicit waters) and MP2 for octamer clusters (eight explicit waters). The final redox potentials were obtained at the MP2/aug-cc-pVTZ (aT) with a self-consistent reaction field (SMD) level using the octamer clusters. The aqueous reduction potentials of the neutral diatomic halogens are predicted within 0.06 V of the experiment for diatomic neutrals. The same agreement of 0.06 V is predicted for the redox potential resulting from dissociation electron attachment of the diatomic halogen anions. The current work extends reduction potentials for multiple redox couples for which no experimental data is available, for example, those containing iodine and the interhalogen anions. F2•- is predicted to dissociate for its lowest energy structure in both the tetramer and octamer clusters to form solvated F-, HF, and OH•.

Evaluation of the coupling of EMACv2.55 to the land surface and vegetation model JSBACHv4

Abstract. We present the coupling of the Jena Scheme for Biosphere–Atmosphere Coupling in Hamburg version 4 (JSBACHv4) to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. With JSBACH, the soil water bucket model in EMAC is replaced by a diffusive hydrological transport model for soil water that includes water storage and infiltration in five soil layers, preventing soil from drying too rapidly and reducing biases in soil temperature and moisture. A three-layer soil scheme is implemented, and phase changes in water in the soil are considered. The leaf area index (LAI) climatology in EMAC has been substituted with a phenology module calculating the LAI. Multiple land cover types are included to provide a state-dependent surface albedo, which accounts for the absorption of solar radiation by vegetation. Plant net primary productivity, leaf area index and surface roughness are calculated according to the plant functional types. This paper provides a detailed evaluation of the new coupled model based on observations and reanalysis data, including ERA5/ERA5-Land datasets, Global Precipitation Climatology Project (GPCP) data and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. Land surface temperature (LST), terrestrial water storage (TWS), surface albedo (α), net top-of-atmosphere radiation flux (RadTOA), precipitation (precip), leaf area index (LAI), fraction of absorbed photosynthetic active radiation (FAPAR) and gross primary productivity (GPP) are evaluated in particular. The strongest correlation (r) between reanalysis data and the newly coupled model is found for LST (r=0.985, with an average global bias of −1.546 K), α (r=0.947, with an average global bias of −0.015) and RadTOA (r=0.907, with an average global bias of 3.56 W m−2). Precipitation exhibits a correlation with the GPCP dataset of 0.523 and an average global bias of 0.042 mm d−1. The LAI optimisation yields a correlation of 0.637 with observations and a global mean deviation of −0.212. FAPAR and GPP exemplify two of the many additional variables made available through JSBACH in EMAC. FAPAR and observations show a correlation of 0.663, with an average global difference of −0.223, while the correlation for GPP and observations is 0.564 and the average global difference is −0.001 kg carbon km−1. Benefiting from the numerous added features within the simulated land system, the representation of soil moisture is improved, which is critical for vegetation modelling. This improvement can be attributed to a general increase in soil moisture and water storage in deeper soil layers and a closer alignment of simulated TWS with observations, mitigating the previously widespread problem of soil drought. We show that the numerous newly added components strongly improve the land surface, e.g. soil moisture, TWS and LAI, while surface parameters, such as LST, surface albedo or RadTOA, which were mostly prescribed according to climatologies, remain similar. The coupling of JSBACH brings EMAC a step closer towards a holistic comprehensive Earth system model and extends its versatility.

Physical modeling of two-phase liquid–gas processes occurring in the refining ladle for Fe–Si alloy refining process

The article presents the results of research carried out using a water model of a refining ladle for the Fe–Si ferroalloys treatment. These studies were aimed at improving the efficiency of refining and homogenization of liquid Fe–Si ferroalloy in the refining ladle by using a new method of blowing gas through a system of nozzles installed at the bottom of the ladle. The obtained results allowed to determine the proper location of the plug at the bottom of the refining ladle and the possibility of using combined blowing. The tests were carried out for a refining ladle with a capacity of 3 m3 using a physical model on a linear scale of 1:3. The gas flow rate used in the model corresponded proportionally to the value previously used in industrial practice and amounted to 26.8 l/min. Experiments were performed for both combined blowing applications and through a purging plug at the bottom of the ladle. In the case of combined blowing, the volume of the gas stream was divided into two blowing sources (lance and purging plug). As a result of laboratory tests, one of the variants was selected and tested in industrial conditions. These studies confirmed the improvement in the efficiency of refining treatment of the FeSi alloy in terms of reducing the carbon and aluminum content in the alloy.x

The temperature of maximum in density of aqueous solutions of nitrate and ammonium salts: Testing the Madrid-2019 force field.

The shift in the temperature of maximum in density (TMD) at room pressure of aqueous solutions of a set of five salts containing NO3- and/or NH4+ groups is studied both through experiments and through molecular dynamics simulations using the Madrid-2019 force field for ions and the TIP4P/2005 model for water. The experiments demonstrate the potential transferability and limitations of the Madrid-2019 force field for nitrate and ammonium ions recently developed by our group at different temperatures and add updated information to the reported datasets of TMDs for strong electrolytes. By using the Despretz law, individual ion contributions are extracted for predictive purposes from the experimental values of the shift in the TMD. Interesting findings for the behavior of the shift in the TMD in nitrate salts expose that this property might be particularly challenging for modelization approaches when dealing with polyatomic species.